An automatic sprinkler system is one of the most widely used devices for fire protection. The sprinklers are activated once the ambient temperature in an environment such as a room or a building exceeds a predetermined value. Once activated, the sprinklers distribute fluid in the room or building. The fluid distribution is believed to cool burning material by conversion of liquid to vapor; the vapor displaces the oxygen supply, thereby tending to smother the fire. Additionally, the fluid distribution may limit the supply of new fuel by moistening materials in the area; and the fluid may lower the ambient temperature in the vicinity by evaporative cooling.
Sprinklers may be designed for different fire protection applications. For occupancy type structures such as an office building, sprinklers have been designed with a relatively small orifice that can deliver a sufficient quantity of water “density” or water flow for a particular area, which can be determined in gallons-per-minute over the square footage of the area. This type of sprinkler is designed for delivery of a desired density that contains a fire within a particular area until other fire fighting techniques can be deployed.
For non-occupancy type structures such as a storage building or warehouse, sprinklers may be designed to suppress or to extinguish a fire shortly after ignition of a fire in a stored commodity. The commodities to be protected, for example, can be encapsulated, unencapsulated or cartoned commodities on plastic or wood pallets. These commodities have been classified by Factory Mutual Global (“FM Global”) as Commodity Classes 1-4 and Plastics. Specific details of each class are given in three FM Global data sheets: FM Global DS 8-0 (September 1998), DS 8-9 (September 2002) and DS 8-24 (September 2000), which are hereby incorporated by reference. Because these sprinklers are preferably designed to actuate very quickly to suppress a fire, they are known as “Early Suppression Fast Response” sprinklers or ESFR sprinklers.
The ability of a sprinkler to suppress fire in a stored commodity is believed to be quantifiable, in part, by the concepts of Actual Delivered Density (“ADD”) and Required Delivered-Density (“RDD”) developed by FM Global. Briefly, ADD is defined as the amount of water flow over an area (gallons per minute over square feet or “GPM/ft2”) which is actually deposited by a particular ESFR sprinkler on top of a combustible package in order to achieve suppression. Through further developments by FM Global, an ADD testing apparatus can determine the ADD of a particular sprinkler configuration. RDD, on the other hand, is the minimum amount of water that must be delivered to the combustible fuel package in order to achieve suppression of a type of fire of a given commodity. RDD tends to increase over time and can be affected by the size of a fire at the time of sprinkler activation. Furthermore, the RDD value of a fire of a particular commodity tends to be fixed and therefore is presumed to be known. Given the assumption that RDD is the minimum amount of water needed to suppress a particular fire, the ADD of a particular ESFR sprinkler configuration can be higher than the RDD in order to effectively suppress a particular fire so that it does not spread beyond an initial ignition area. Thus, a particular fire protection system can be provided with sprinklers having an ADD greater than the RDD of the commodity that are to be protected.
The Performance requirements of ESFR sprinklers are set forth in Underwriters Laboratories, Inc., (“UL”) Standard for Early-Suppression Fast-Response Sprinklers 1767 (Section 7, Rev. Jan. 24, 2000), and, such ESFR sprinklers, are typically installed in accordance with the requirements of the National Fire Protection Association (“NFPA”) standards including NFPA 13 (2002), NFPA 30 (2000), NFPA 30B (2002). Factory Mutual Global (“FM Global” or “FM”) also has standards for ESFR sprinklers, particular, FM Approval Standard Class Nos. 2008, 2026, 2032 (June 2000 and Suppl. September 2000) that set forth performance requirements of such ESFR sprinkler, and FM Global Property Loss Prevention Data Sheets including DS 2-2 (September 2001), DS 8-9 (September 2002), DS 8-24 (September 2000) that address installation standards for the ESFR sprinkler. All of these current ESFR standards and all earlier ESFR standards of either organization are incorporated by reference herein in their entirety (hereafter referred to as “the Standard Documents”).
The standards also specify a particular response time for ESFR sprinklers. Although ordinary or standard sprinklers are considered to have a response time index (“RTI”) of 100 meter1/2second1/2 (“m1/2sec1/2”) or more, existing ESFR sprinklers must exhibit a response time indices of less than 40 m1/2sec1/2. Response time can be measured in various ways. FM Global and Underwriters Laboratories (“UL”) use a combination of temperature ratings and response time indices to insure adequately fast response is being provided. The response time indices or “RTI” is a measure of thermal sensitivity and is related to the thermal inertia of a heat responsive element of a sprinkler. RTI is believed to be related to a heat transfer coefficient “h” and the velocity “u” of hot gas flowing past a heat responsive trigger element. For fast-growing industrial fires of the type to be protected by ESFR sprinklers, it is believed that the RTI of less than 40 m1/2sec1/2 and temperature rating of 165° F. or 214° F. of the trigger are sufficient to insure adequately fast sprinkler response. As such, FM 2008 and UL 1767 specify an RTI of about 36 m1/2sec1/2. By determining the time at which the trigger is activated in a heated flow stream at a predetermined temperature, the RTI of a specific heat responsive trigger can be determined by a standardized test apparatus developed by Factory Mutual Global as outlined in the Standard Documents.
The rapid response and larger flow orifices of these sprinklers were believed to be designed for suppression of fires in warehouses with 30 feet ceilings where flammable commodity is piled up to approximately 27 feet high in racks. Requirements for the installation and use of ESFR sprinklers are included in the Standards Documents. It is believed that the existing ESFR sprinklers for warehouses with the higher ceiling height are limited to a pendent configuration having the necessary ADD to suppress a fire of a given RDD at the ceiling height of 35 feet for upright ESFR sprinklers and 45 feet for pendent ESFR sprinklers. For example, the discharge coefficient (or “K” factor) of an existing pendent type ESFR-instead of an upright—sprinkler is nominally between 11-25, where the K-factor is calculated by dividing the flow of water in gallons per minute (GPM) through the sprinkler by the square root of the pressure of water supplied to the sprinkler in pounds per square inch gauge (i.e., GPM/(psig)1/2). Upright type ESFR sprinklers are available; however, the K-factor of these ESFR upright sprinklers is limited to 14 or less and further require, among other things, that a minimum operating pressure of 50 pound-per-square inch gauge (psig) or greater be provided.
It is believed that the existing upright ESFR sprinklers do not provide, at low operating pressures, a sufficient quantity of water to produce early suppression of a fire in a commodity to protect warehouses with the higher ceiling height. However, it is believed that the existing ESFR upright sprinklers are unsatisfactory because, in order to achieve the necessary density, they require a minimum operating pressure of at least 50 psig for a ceiling height of 30 feet with storage height of approximately 27 feet and at least 75 psig for a ceiling height of 35 feet and storage height of approximately 32 feet.